1. Field of the Invention
The present invention relates to light emitting diode assemblies that are useful to illuminate the interior of a vehicle, such as an aircraft, and more particularly to tubular assemblies having a housing that contains a plurality of light emitting diodes.
2. Description of the Related Art
Aircraft cabins have been illuminated by fluorescent lighting systems. The disadvantages of that type of lighting include the relatively short life of the fluorescent lamp, significant weight of the ballast, heat production, generation of radio frequency interference (RFI), and fragility.
One solution to counter the problems identified above has been to use an assembly of light emitting diodes (LED). U.S. Pat. No. 6,158,882 describes an aircraft lighting system which employs a plurality of LED's mounted in a linear array to form a lighting strip. Such a strip can be used to wash a wall or ceiling of the aircraft cabin with light. The electrical power to illuminate the LED's is furnished from a DC power supply that includes a mechanism for adjusting the voltage to control the level of illumination provided by the lighting strip. This enables the light intensity, or brightness to be varied depending upon the outside light level and activity of the passengers. When the aircraft is flying in daylight, the LED lighting strip usually is driven at a voltage level which provides maximum illumination. At nighttime, that maximum illumination level may interfere with the ability of occupants to sleep or see through the plane's windows, especially upon landing. Therefore, a lower interior illumination level is preferred at night.
In addition to incorporating LED strips into new aircraft, it is desirable to retrofit older aircraft with this type of lighting. Many older planes have conventional fluorescent lighting system that uses lamp tubes with a pair of electrical connector pins at each end. Each pair of pins fits into a socket of the light fixture which mechanically holds the fluorescent tube in place, as well as electrically connects the tube to the power source. A fluorescent light fixture can be readily modified to accept an LED lighting strip by removing the ballast and connecting the 110 VAC power from the aircraft directly to the sockets. The LED lighting strip for this application has a full wave rectifier to convert the alternating current into direct current. A sufficient number of light emitting diodes are connected in series so that voltage across each one conforms to the diode's rating.
A standard fluorescent lamp tube is mounted in the light fixture by sliding the connector pins into end sockets and then turning the tube 90° so that the pins engage electrical contacts in the sockets. The fluorescent lamp tube emits light omnidirectionally and its orientation in the sockets is of no consequence. Specifically, it does not matter which pin is inserted first into the socket or the direction that the tube is rotated to make electrical contact. Thus even though the position of the sockets with respect to the cabin walls may vary a fluorescent lamp tube can be used with a different aircraft makes and models.
However, that is not the case for LED lighting strips in which each LED emits light at a narrowly angled conical path. Therefore, a LED lighting tube retrofitted into the existing fluorescent light fixture may not be oriented to emit light in the desired direction within the aircraft. Thus a need exists to be able to adjust the orientation of the LED lighting tube in the sockets of a modified fluorescent lighting system.